This invention relates in general to controllers for electric trailer brakes and in particular to a deceleration sensor for an electric brake controller.
Towed vehicles, such as recreational and utility trailers adapted to be towed by automobiles and small trucks, are commonly provided with electric brakes. The electric brakes generally include a pair of brake shoes which, when actuated, frictionally engage a brake drum. An electromagnet is mounted on one end of a lever to actuate the brake shoes. When an electric current is applied to the electromagnet, the electromagnet is drawn against the rotating brake drum which pivots the lever to actuate the brakes. Typically, the braking force produced by the brake shoes is proportional to the electric current applied to the electromagnet. This electric current can be relatively large. For example, the electric brakes on a two wheeled trailer can draw six amperes of current when actuated and the electric brakes on a four wheeled trailer can draw 12 amperes of current.
Automotive industry standards require that electrically-actuated vehicle brakes be driven against the ground potential of the vehicle power supply. Accordingly, one end of each of the towed vehicle brake electromagnets is electrically connected to the towed vehicle ground and the towed vehicle ground is electrically connected to the towing vehicle ground. The other end of each of the brake electromagnets is electrically connected through an electric brake controller to the towing vehicle power supply.
Various electric brake controllers for towed vehicle electric brakes are known in the art. For example, a variable resistor, such as a rheostat, can be connected between the towing vehicle power supply and the brake electromagnets. The towing vehicle operator manually adjusts the variable resistor setting to vary the amount of current supplied to the brake electromagnets and thereby control the amount of braking force developed by the towed vehicle brakes. An example of such a controller is disclosed in U.S. Pat. No. 3,740,691.
Also known in the art are more sophisticated electric brake controllers which include electronics to automatically supply current to the brake electromagnets when the towing vehicle brakes are applied. Such electronic brake controllers typically include a sensing unit which generates a brake control signal corresponding to the desired braking effort. For example, the sensing unit can include a pendulum which is displaced from a rest position when the towing vehicle decelerates and an electronic circuit which generates a brake control signal which is proportional to the pendulum displacement. One such sensing unit is disclosed in U.S. Pat. No. 4,726,627. Alternately, the hydraulic pressure of the brake fluid in the towing vehicle""s braking system or the pressure applied by the driver""s foot to the towing vehicle""s brake pedal can be sensed to generate the brake control signal. A pressure transducer for sensing the brake fluid pressure is disclosed in U.S. Pat. No. 4,279,162, while a brake pedal pressure sensor is disclosed in U.S. Pat. No. 4,380,002.
Known electronic brake controllers also usually include an analog pulse width modulator. The input of the pulse width modulator is electrically connected to the sensing unit and receives the brake control signal therefrom. The pulse width modulator is responsive to the brake control signal for generating an output signal comprising a fixed frequency pulse train. The pulse width modulator varies the duty cycle of the pulse train in proportion to the magnitude of the brake control signal. Thus, the duty cycle of the pulse train corresponds to the amount of braking effort desired.
Electronic brake controllers further include an output stage which is electrically connected to the output of the pulse width modulator. The output stage typically has one or more power transistors which are connected between the towing vehicle power supply and the towed vehicle brake electromagnets. The power transistors function as an electronic switch for supplying electric current to the towed vehicle brakes.
The output stage is responsive to the pulse width modulator output signal to switch the power transistors between conducting, or xe2x80x9conxe2x80x9d, and non-conducting, or xe2x80x9coffxe2x80x9d, states. As the output transistors are switched between their on and off states in response to the modulator output signal, the brake current is divided into a series of pulses. The power supplied to the towed vehicle brakes and the resulting level of brake application are directly proportional to the duty cycle of the modulator generated output signal. A typical electronic brake controller is disclosed in U.S. Pat. No. 4,721,344.
Recently, microprocessors have been incorporated into electronic brake controllers. The microprocessor replaces the analog pulse width modulator described above. The microprocessor is connected directly to the controller output stage and switches the output transistors between their on and off states as a function of the brake control signal. Such a unit is disclosed in U.S. Pat. No. 5,620,236.
This invention relates to a deceleration sensor for an electric brake controller.
As described above, it is known to use a pendulum device to generate a brake control signal which is proportional to the deceleration of a towing vehicle. Because the pendulum rest position is determined by gravity, it is necessary to level the pendulum when the controller is mounted upon a vehicle dashboard in a nonhorizontal position. Accordingly, it would be desirable to provide a structure for supporting the pendulum that would allow a maximum amount of adjustment to compensate for a variety of mounting positions.
The present invention contemplates a device for sensing the deceleration of a vehicle which includes a housing adapted to be secured to the vehicle. The housing includes a pair of spaced apart supporting members with a U-shaped bucket suspended between the housing support members and pivotable about an axis. A pendulum is suspended within the bucket and also pivotable about the same axis. A positioning device is carried by the housing and connected to the bucket. In the preferred embodiment, the positioning device includes a crank which is connected to the bucket and operable to rotate the bucket relative to the housing. The positioning device is operable to rotate the bucket about the axis relative to the housing in either a forward or a rearward direction with the bucket being rotatable sufficiently in either the forward or rearward direction such that at least of portion of the bucket extends beyond both of housing supporting members.
At least one of the housing support members has a recess formed therein, the recess receiving a portion of the crank whereby the amount of rotation of the bucket about the pivot pin is increased over prior art sensor designs. The housing further includes a cross member supported by a pair of arms which extend from the housing support members. The cross member is urged by the arms against a portion of the bucket such that the bucket is frictionally retained in a particular position relative to the housing.
It is also contemplated that the device includes a carrier mounted upon the bucket, the carrier having a slot formed therein which slidingly receives and frictionally retains a Hall Effect Device. The end of the pendulum opposite from the pivot carries a permanent magnet. The permanent magnet cooperates with the Hall Effect Device upon movement of the pendulum to cause the Hall Effect Device to generate a voltage which is proportional to the deceleration of the vehicle.
In the preferred embodiment, the device is included in an electric brake controller installed upon a towing vehicle. The voltage generated by the Hall Effect Device upon deceleration of the towing vehicle is utilized by the brake controller as a brake control signal for controlling a set of electric wheel brakes mounted upon a towed trailer. The electric brake controller can have an outer housing with the device mounted inside the outer housing. In such a case, the outer housing has an aperture formed therethrough with an end of the crank extending through the outer housing aperture. An adjustment lever is formed upon the extended end of the crank. A vehicle operator can manipulate the adjustment lever to move the bucket relative to the housing in order to position of the Hall Effect Device relative to the pendulum magnet.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.